In an attempt to translate the progress we have made in understanding the basic biology of immune reconstitution, we are engaged in clinical trials of tumor immunization and immune reconstitution for patients with high risk pediatric sarcomas. Currently two trials are open (97-C-0050 and 97-C-0052). In both trials, tumor specific immunization is undertaken by the use of peptide pulsed dendritic cells. The peptide which is used is derived from the breakpoint region of the tumor specific translocations found in Ewing's sarcoma [t(11;22)] and alveolar rhabdomyosarcoma [t(2;13)]. In the first series of patients, 16 patients receive autologous elutriated monocytes which were pulsed with the peptides and high does IV interleukin-2 on 97-C-0050. We observed one mixed clinical response and one biologic response in this group. We also identified significant problems with T cell depletion in heavily pretreated patients as well as very large tumor burdens using standard Phase I entry criteria. The results of this trial concluded that while the responses seen were of interest, and the toxicity of this approach was minimal, future trials should focus on recruiting patients with smaller tumor burdens and more optimal immunity so that the potential benefits of immunotherapy may be better tested. These results are currently in press (A Pilot Trial of Tumor-Specific Peptide Vaccination and Continuous Infusion Interleukin - 2 in Patients with Recurrent Ewing's Sarcoma and Alveolar Rhabdomyosarcoma: an Inter-Institute NIH Study R Dagher, LM Long , EJ Read, SF Leitman, CS Carter, M Tsokos, TJ Goletz, N Avila, JA Berzofsky , LJ Helman, CL Mackall, Medical and Pediatric Oncology, In Press). In an effort to improve on these results we began studies in 1999 using peptide pulsed dendritic cells which had been derived by culture of monocytes with GM-CSF and IL-4. We enrolled a total of 4 patients with low tumor burdens and relatively good immunity on this trial but saw no clinical or biological responses. We also enrolled a total of 9 patients on a second clinical trial (97-C-0052) which utilized the same peptide pulsed vaccine as well as autologous T cell transfusion as a means for immune reconstitution. Importantly these patients are at high risk for disease recurrence, but are not required to have evaluable disease at the time of immunotherapy. Endpoints are evidence for immune reconstitution and measurable immune responses to the vaccine. We noted one patient with a transient biologic response to the vaccine and one patient with a positive immune reconstitution response. Several of the nine patients were not evaluable for immune reconstitution due to young age or insufficient T cell depletion at the time of enrollment. Of these nine patients, six remain alive and three remain free of disease, but whether the immune based therapies contributed in any way to this outcome remains unclear. Based upon these results, we continued to believe that we could further optimize the dendritic cells used for immunization and thus developed an M-CRADA with Immunex Corp. to obtain CD40 ligand for further maturation of the dendritic cells. The newly amended trials using CD40 ligand matured DCs began enrollment in January 2001. Thus far, one patient without T cells for immune reconstitution (97-C-0050) has completed immunotherapy with CD40 ligand matured DCs and showed no evidence for a biologic response and tumor progression. Furthermore, six patients have been enrolled and begun therapy with T cell infusions and CD40 ligand matured DCs. One showed rapid progression and has died of disease. The rest are without disease recurrence and are currently being evaluated for evidence of immune responses (97-C-0052). In general, these protocols have accrued steadily reflecting an interest within the pediatric oncology community in developing immune based therapies for these diseases. Furthermore, we are currently learning much about the approaches which can be used to optimize dendritic cell vaccines and well as immunorestorative therapies. It is anticipated that we will remain involved in immune based clinical trials for these diseases but that the specifics of the protocols will evolve based upon the rapid advances in basic sciences and technology development which are occurring. AIDS RELATED 50%